Interlaced Fields?

[Eltrion]

So I have an odd and somewhat technical question.
How does the timing of frames relate to the fields displayed on an interlaced CRT TV?
Is it 60 fields per second each correlating one to one with a debug frame? (This doesn't make sense to me as that's normally considered 30fps, right?)
Or is it 120 fields per second each updating first one field to a frame and then the other?
Then there is a third possibility one field is synced with the frames and the other one is matched to the X.5 sub frame.

Does anyone know enough about this subject to clear this up for me.

 

[Sixfortyfive]

480i on left, 480p on right:

480p is 60 frames per second.
480i is 60 fields per second (basically 60 "half-frames" per second).

Gameplay is identical no matter which video format you're using, but in 480i, you're basically only seeing half of each frame (either only the odd lines, or only the even lines).

This is only accurate for CRTs / interlaced displays. If you connect a 480i source to a progressive scan only TV (e.g. every modern flatpanel), then the TV will deinterlace the video feed in some manner, and most are terrible at this.

 

[Eltrion]

So the first suggestion then. Hmm. I would have figured interlace tearing to be more obvious to the naked eye then.

Seems slightly dishonest to call it 60 fps then. But then it looks far nicer than 30 fps in a progressive scan monitor, so...

Oh well. I think it looks nice.

 

[Sixfortyfive]

It's easy to spot if you know what to look for. It's most obvious in scenes with fast movement or abruptly changing HUDs (e.g. timer sprites).

It's more obvious on non-interlaced screens and capture equipment that don't attempt to de-interlace the footage. These devices update the frame two fields at a time at only 30 times per second (instead of alternating individual fields at 60 times per second), like so: